Known Excel Limitations for Values with More Than 16 Digits
When you open a CSV directly, Excel treats long numbers as numeric values and shows them in scientific notation. This can cause a loss of precision for numbers longer than 16 digits and may cut off digits beyond that. Even if apostrophes or double quotes are used as text qualifiers, the text within them is still recognized by Excel heuristics as a number and an additional formatting hint must be provided. This heuristics is known in Excel as the "General" format. One way to work around this limitation is to always open CSV files using Excel's multistep Text Import Wizard. The wizard enables you to set column formatting in the last step ("Text" format). Or, you can use another office suite like LibreOffice, which always shows the import wizard for CSVs.